Styrene is a commodity chemical commonly used in the manufacture of many types of consumer products including, for example, plastics (polystyrene and co-polymers thereof), rubbers, and resins. Styrene-based consumer products are routinely used in food, safety and health applications. Stability, purity and appearance of the styrene monomer may be important for the intended end use in these and other applications.
Styrene monomer purity may determine the properties of the styrene-based material ultimately produced. For example, impurities may inhibit the ability of styrene to polymerize to a desired polymer molecular weight and impact the mechanical properties of the polymer so obtained. Color of the polymer may also be impacted by impurities. The presence of impurities may additionally influence the stability of styrene monomer during storage due to the reactive nature of the styrene vinyl group. Premature styrene polymerization or oligomerization not only leads to styrene loss, but also to potential fouling of a styrene processing system.
Catalytic dehydrogenation of ethylbenzene is the most common method by which styrene is produced. Styrene produced in this manner is a colorless liquid with a very low sulfur content. Styrene is also present in hydrocarbon streams such as, for example, pyrolysis gasoline. Although separation of styrene from pyrolysis gasoline and other hydrocarbon streams has typically been considered difficult, recent advances in separations technology have enabled styrene to be obtained, albeit at significant cost. For example, styrene can be recovered from raw pyrolysis gasoline derived from the steam cracking of naphtha, gas oils and natural gas liquids (NGL). However, the quality of styrene directly obtained from a hydrocarbon stream such as pyrolysis gasoline is typically inferior to that obtained by dehydrogenation of ethylbenzene.
In view of the foregoing, efficient methods to remove impurities from a hydrocarbon stream containing styrene and other vinyl aromatic compounds would be desirable in the art. With the availability of such impurity removal methods, non-conventional hydrocarbon streams such as pyrolysis gasoline may become a more attractive feedstock for production of high value commodity chemicals such as, for example, styrene. In the case of styrene and other vinyl aromatic compounds, such purification methods would advantageously lead to enhanced monomer stability, prevent fouling of processing systems and lead to greater reproducibility during polymerization reactions.